This invention relates to jet drop printers and applicators, and more particularly to the precise control of the density of the fluid application by controlling the time interval that charge potential is applied to the charge electrode. Jet drop printers are well known. Typical examples of the prior art of interest in connection with this invention may be found in U.S. Pat. Nos. 4,087,825 to patentees Chen et al; 3,787,881 to patentee Duffield; 3,588,906 to patentees VanBrimer et al; 3,803,628 to patentees Van Brimer et al; 4,033,154 to patentee Johnson; 3,915,113 to patentees Paton et al; 3,373,437 to patentees Sweet et al; 3,739,393 to patentees Lyon et al; 3,882,508 to patentee Stoneburner; and 4,095,232 l to patentee Cha. The control of the density of an applied coating has been a serious problem. Generally, in the prior art, the density of fluid application has been controlled by turning on the drop stream for an arbitrary period of time. More sophisticated systems have used a tachometer measuring substrate travel by which to vary, that is, lengthen or shorten the set period of time in accord with the substrate movement. An example of this is illustrated by U.S. Pat. No. 3,803,628. Generally, the best control over the density of coating possible with prior art devices has only been to within quite a few drops per dot.